Messing With Numbers

What patterns do you see here?
8 x 20 = 160
4 x 40 = 160
2 x 80 = 160
16 x 10 = 160
32 x 5 = 160
64 x 2.5 = 160
128 x 1.25 = 160

It is fair to double one number if you cut the other one in half. Why?

18 x 5	16 x 5	26 x 5	460 x 5
10x5=50 8x5=40 50+40=90	Replace this text with how you would do this problem in your head.	Try this one and type in a solution.
18 x 5 is the same as 9 x 10 (because I cut 18 in half and doubled 5) 9 x 10 = 90